Engine oils are finished crankcase lubricants intended for use in automobile engines and diesel engines and consist of two general components; a lubricating base oil and additives. Lubricating base oil is the major constituent in these finished lubricants and contributes significantly to the properties of the engine oil. In general, a few lubricating base oils are used to manufacture a variety of engine oils by varying the mixtures of individual lubricating base oils and individual additives.
Numerous governing organizations, including Original Equipment Manufacturers (OEM's), the American Petroleum Institute (API), Association des Consructeurs d' Automobiles (ACEA), the American Society of Testing and Materials (ASTM), International Lubricant Standardization and Approval Committee (ILSAC), and the Society of Automotive Engineers (SAE), among others, define the specifications for lubricating base oils and engine oils. Increasingly, the specifications for engine oils are calling for products with excellent low temperature properties, high oxidation stability, and low volatility. Currently, only a small fraction of the base oils manufactured today are able to meet these demanding specifications.
Lubricating base oils are petroleum derived or synthetic hydrocarbons having a viscosity of about 2.5 cSt or greater at 100° C., preferably about 4 cSt or greater at 100 C; a pour point of about 9 C or less, preferably about −15 C or less; and a VI (viscosity index) that is usually about 90 or greater, preferably about 100 or greater. Premium base oils will have a VI of at least 120. Lubricating base oils intended for preparing finished lubricants should have a Noack volatility no greater than current conventional Group I or Group II light neutral oils.
The term “base oil” refers to a hydrocarbon product having the above properties prior to the addition of additives. Base oils are generally recovered from the higher boiling fractions recovered from the vacuum distillation operation. They may be prepared from either petroleum-derived or from syncrude-derived feedstocks. “Additives” are chemicals which are added to improve certain properties in the finished lubricant so that it meets the minimum performance standards for the grade of the finished lubricant. For example, additives added to the engine oils may be used to improve stability of the lubricant, lower its viscosity, raise the viscosity index, and control deposits. Additives are expensive and may cause miscibility problems in the finished lubricant. For these reasons, it is generally desirable to lower the additive content of the engine oils to the minimum amount necessary to meet the appropriate requirements.
There are two principal categories of engine oil additives: DI additive packages (Detergent Inhibitor additive packages) and VI improvers (Viscosity Index improvers). DI additive packages serve to suspend oil contaminants and combustion by-products as well as to prevent oxidation of the oil with the resultant formation of varnish and sludge deposits. VI improvers modify the viscometric characteristics of lubricants by reducing the rate of thinning with increasing temperature and the rate of thickening with low temperatures. VI improvers thereby provide enhanced performance at low and high temperatures. In many multigrade engine oil applications VI improvers have to be used with DI additive packages. Engine oil additive packages are available from additive suppliers. Additive packages are formulated such that, when they are blended with a base oil or base oil blend having the desired properties, the resulting engine oil is likely to meet a specified engine oil service category. Specific engine oil service categories that are used, or being developed, today include ILSAC GF-3, ILSAC GF-4, API CI-4, and API PC-10.
The minimum specifications for the various viscosity grades of engine oils is established by SAE J300 standards as revised in June 2001. Base oils prepared from products made by the Fischer-Tropsch synthesis reaction are characterized by a very low sulfur content and excellent stability making them excellent candidates for blending into high quality finished lubricants. Unfortunately, finished lubricants blended from Fischer-Tropsch derived base oils generally display poor low temperature properties, particularly low temperature pumpability. Consequently, Fischer-Tropsch derived base oils have had difficulty passing the stringent mini-rotary viscometer (MRV) TP-1 viscosity specifications under SAE J300 as revised 2001.
ILSAC GF-3 refers to an engine oil service category of automotive gasoline engines. This specification became official on Jul. 1, 2001. ILSAC GF-4 refers to a new engine oil service category of automotive gasoline engines that was approved on Jan. 8, 2004. It became official on Jul. 1, 2004. This category introduces new sulfur limits measured by standard test method ASTM D 1552. The maximum sulfur limit for 0W-XX and 5W-XX oils is 0.5 wt %. The maximum sulfur limit for 10W-XX oils is 0.7 wt %. An engine oil meeting GF-4 requirements will also meet GF-3 requirements, but an engine oil meeting GF-3 requirements may not meet the requirements for a GF-3 engine oil.
A multigrade engine oil refers to an engine oil that has viscosity/temperature characteristics which fall within the limits of two different SAE numbers in SAE J300. The present invention is directed to the discovery that multigrade engine oils meeting the specifications under SAE J300 as revised 2001, including the MRV TP-1 viscosity specifications, may be prepared from Fischer-Tropsch base oils having a defined cycloparaffin functionality when they are blended with a pour point depressing base oil blending component and an additive package.
As used in this disclosure the word “comprises” or “comprising” is intended as an open-ended transition meaning the inclusion of the named elements, but not necessarily excluding other unnamed elements. The phrase “consists essentially of” or “consisting essentially of” is intended to mean the exclusion of other elements of any essential significance to the composition. The phrase “consisting of” or “consists of” is intended as a transition meaning the exclusion of all but the recited elements with the exception of only minor traces of impurities.